I uninstalled the game again, deleted every reference to it in the registry, and removed any Witcher-related folder I could find on my HD. Then I also removed Daemon Tools just to be sure, and rebooted. Reinstalled the game and applied the patch. It's now about 45 minutes later, and it hasn't complained. Hopefully that did the trick. I would be a bit upset if this was caused by Daemon Tools though. Not only was the error message misleading in that case, but it also means I had to uninstall an application I use for legal purposes. Rest assured it's going to be reinstalled later, but for now I'll be happy if The Witcher runs.